How does a fish regrow a missing tail fin?

Frogs, newts, lizards and some fish can grow new parts -- why not people?

If a zebrafish loses a chunk of its tail fin, it'll grow back within a week. Like lizards, newts, and frogs, zebrafish can replace parts of their body. Some of the parts they can replace are very complicated. A tail fin, for example, is a complex piece of work. It helps the fish move, swim and fight off enemies. A tail fin for a fish is as important as an arm or leg is for a person.

The question of how cold-blooded animals re-grow missing tails has fascinated scientists. They also wonder if people, and other warm-blooded animal such as dogs and cats, might still be able to regrow body parts, just as they were able to grow their bodies out of scratch when they were in their mother's womb. Perhaps the ability to grow new body parts is just turned off and hidden away. Perhaps there's a way to turn it on again to help people and animals who are injured.

People are can make new blood, bone, and skin. They can re-grow part of their livers. Their minor cuts and scrapes will heal on their own and their broken bones can be fixed with the help of a doctor. Finding out how zebra fish re-grow their tails might provide information that could someday be used to find new ways to treat people who have been badly hurt.

Scientists know that cells, the building blocks of all living things, can send messages to each other. These messages tell the cells what jobs to do. For example, these messages can ask a cell that already has a job to do something else. Or they tell a cell what to do if it doesn't already have an assignment.

Certain kinds of cells act like conductors of an orchestra. They direct how a baby grows inside its mother's womb. These cells send messages to other cells to tell them to become the baby's backbone, or the baby's eyes or skin, and so on until the baby is complete and ready to be born. There are also signals that say, "Enough already!" These signals stop parts of the body from growing more after they reach the right size and shape and have what they need to work well. Even then, adults still can replace some parts of their body, such as blood cells and skin.

Scientists in a laboratory at the University of Washington think that signals that tell a baby how to grow inside its mother might be like the signals that help a fish regrow its missing tail. These scientists are Cristi Stoick-Cooper, Randy Moon, and Gilbert Weidinger. Gilbert is now working at a lab in Dresden, Germany, that also studies these special signals.

Fish can do something that people can't: They can form a little nub of cells that direct the growth of a new tail, much the same way that a boss tells workers how to build a new room on a house. People are unable to form these little nubs of "boss cells," which is perhaps why people can't re-grow their arms or legs.

Cristi, Randy, Gilbert and their co-workers in their lab were the first people to find a gene that stops a new fish tail from growing. Genes are codes passed from parent to child that contain a lot of information about growing and living. In this case, the gene found in the lab has information on how to stop new growth from getting out of hand. This keeps the fish's tail from growing too big, like Pinocchio's nose. This is an exciting discovery, because the scientists think this same gene might also be keeping people and animals like cats and dogs from being able to grow new body parts.

The UW scientists have reported their findings on this gene and their new information on cell signals to other scientists in the Dec. 21 issue of the scientific magazine, Development.

If scientists could learn a way to turn off this gene and turn on the correct cell-to-cell signals, they might be able to find new ways to treat people who have been injured or who have illnesses that make parts of their bodies not work well. For example, someday in the future scientists might be able to help people who have trouble moving. They might find a way to help people grow new connections between their nerves so that they can use their legs or hands again, or help people with poor vision grow new parts of their eyes so that they can see better.